Both of the engines in my jet boat have suffered the safe fate: cooling problems let to piston expansion and rubbing on the rear cylinder. It appears the main problem was a pinched cooling line from the rear of the head , under the pipe, to the nipple on the u-shaped exhuast pipe. On both engines, this cooling line was pinched under the exhaust pipe, cutting off coolant flow to the rear of the engine.

Is this a common problem with the 1100/1200 engines? It seems strange that both had the same issue. I'm in the process of re-building the engines now, and will route the coolant line elsewhere when I re-install.